The invention relates to a printing device for printing on printing material in the form of a roll, especially rolls of labels and/or receipts, including a print head unit and a transporting device for the printing material.
The purpose of the printing device incorporating the transporting device for the printing material (which is also referred to hereinafter as a roll printer or printer) is to wind off a strip of receipts or a strip of labels or the like from a roll, these receipts or labels that are to be printed upon being made of paper or synthetic material, to transport the strip through the roll printer and then, following the printing process, to eject the printed strip of printing material that is now in the form of a printed document from the printer for manual or automatic removal. In dependency on the nature of the document that is to be printed, there are different types of rolls which impose differing demands on the transporting device for the printing material during the transportation thereof through the printer. The present invention is mainly concerned with three different types of rolls which can be processed by the device in accordance with the invention:                Receipt or label rolls comprising a running, non-adhesive strip of printing material.        Self-adhesive label rolls comprising a backing strip, wherein the labels are stuck to a backing strip and are separated from one another.        Self-adhesive label rolls without a backing strip, so-called “linerless” label rolls, comprising a running, adhesive strip of printing material.        
In the case of all three types of strips of material, the functional elements of the printing device that come into contact with the strip of printing material during the transportation process, especially the print head, the transport rollers, including the print roller, the stripping edge and the drawing off roller, are subjected to heavy soiling from abraded paper and residual remnants of the adhesive. Consequently, for functional reasons, it is necessary to clean these parts at relatively short intervals. Moreover, these parts are also subject to wear so that replacement thereof is necessary after a certain service life.
A printer is known from WO 98/34791 AI, wherein a thermal print head together with a rigidly attached fixing member forms a unit which is held in position by means of a permanent magnet. Replacement of the print head in the event of failure or for cleaning purposes cannot be effected without loosening screws, i.e. it cannot be dismantled without tools.
In addition, the transport rollers for the printing material and the drawing off edge cannot be dismantled without tools and must be adjusted thereafter, and they can only be accessed with difficulty for cleaning purposes.
A pressure roller is known from U.S. Pat. No. 4,900,175, wherein the hollow axle thereof is provided with recesses and a groove at one side. This is inserted in the axial direction into a matching central boring of a drive wheel where it is a snug-fit, and it latches therein in the functional position. The pressure roller can easily be dismantled in the axial direction by releasing the latch.
A printer having an easily dismantled print roller is known from DE 40 04 930 AI. The print roller, which is mounted at each end in the printer frame, can be removed from the printer perpendicular to the axis of the pressure roller after actuating two release buttons. The problem here, however, is that in the case of this construction, replacement of the printing material or a fresh insertion thereof causes difficulties and is an extremely laborious process.
The important thing for this purpose is a freely accessible, open side for the insertion of the strip of printing material.